The present invention is related to techniques for penetration of an object with a shaft and more particularly to apparatuses and methods for determining the penetration depth of a hypodermic needle.
When inserting a long structure into an object, such as a needle into the tissue of a patient, it is often necessary to know how deep the penetration is. Penetration past the required depth for a desired result wastes effort and causes undue discomfort to the patient. Often the information is needed in a short time because further penetration may cause unnecessary damage to the object and it is desirable to stop the penetration once a predetermined depth is reached. For example, the analysis and quantification of blood components is an important diagnostic tool for better understanding the physical condition of a patient and blood samples need to be obtained by inflicting a wound by a needle or lancet. Inserting the needle or lancet to a depth deeper than necessary produces excessive pain and trauma to the skin tissue. In patients such as diabetics, who have to sample blood often, any excessive pain or tissue trauma is a disincentive to comply with the blood sampling routine.
The skin is consisted of two layersxe2x80x94the epidermis and the dermis. The capillary structures connected to the arterial and venous vascular beds rise vertically and are located in the dermis layer. The neural sensors such as Meissner""s corpuscles and free nerve endings are also located in the dermis. Layers of subcutaneous tissues lie below the dermis. The supply arterial and venous capillaries are located laterally in this tissue bed. There is also adipose tissue interleaved with afferent and efferent nerve fibers along with their associated sensors interwoven within the vascular bed. The thicknesses of these tissue layers differ from individual to individual. Currently, commercially available needle or lancet for puncturing skin have preset penetration depth based on experimental data from lancing, Thus, there is no certainty that the optimal depth of penetration is reached every time such a needle or lancet is used. To avoid unsuccessful blood sampling due to inadequate depth, a patient often overpenetrates the skin, causing unnecessary pain.
What is needed is a needle or lancet for sampling blood that can be used for inserting to the optimal depth without over or under penetration. Similarly, there is a need in other penetration applications for inserting a long shaft into an object without over or under penetration.
In the present invention, the depth of penetration of an elongated structure into an object is determined by an impedance sensor that senses the impedance of the material penetrated by the elongated structure at the tip of the elongated structure.
In one aspect, the present invention provides an apparatus having a shaft for penetration into an object which has impedance that varies according to the depth under a surface of the object. The apparatus contains a shaft that includes a shaft body having a tip for penetration and two conductive ends near the tip. The two conductive ends are near the tip such that a change of impedance of the material of the object sensed between the conductive ends will provide information on whether the desired depth of penetration has been reached.
This invention is especially applicable in obtaining blood from a patient by puncturing the skin because a shaft of the present invention takes advantage of the electrical impedance differences between deeper layers of skin tissue relative to the more shallow upper layer. The impedance can be monitored by, for example, a metallic needle that pierces the layers of skin tissue. When the needle initially penetrates into the outer epidermis and dermis layers of the skin, an initial high impedance is seen. A decline in the impedance is observed as the needle approaches the adipose layer.
Using the apparatus, including the shaft of the present invention, optimal penetration into an object that has electrical impedance which varies with penetration depth can be achieved. In the case of obtaining blood from a patient by inserting a needle into the skin, this can minimize the trauma and pain of overpenetration, as well as avoid the frustration and pain of unsuccessful blood sampling because of inadequate penetration. Such reduction of discomfort and tissue damage can significantly improve the compliance of patients with a blood sampling routine, for example.